"Let's think just how legal and ethical our behaviour would be if we invited to Moscow the head of a friendly state and at the same time raised the issue of him leaving power?

"Syria is a sovereign country, Bashar al-Assad is a president elected by the people. So do we have the right to discuss with him these issues? Of course not," Putin said in an interview with the Interfax and Anatolia news agencies.

World powers are to hold another round of talks on the Syrian conflict in Vienna this weekend.

Putin reiterated that Russia's bombing campaign in Syria would last for the duration of an offensive by the Syrian army.

"So the duration of our military's stay will be determined solely by the implementation of this goal," Putin said.

The Russian president also said the "possible risks and consequences" of Russia's Syrian intervention have been addressed multiple times.

On September 30, Russia launched a bombing campaign in Syria, saying it needed to target Islamic State jihadists, but the West has accused Moscow of seeking to prop up Assad's regime and hitting moderate rebels.

The Islamic State group claimed responsibility for the attack in an apparent act of revenge for Russia's Syria intervention.

Sources close to the probe have told AFP that experts involved in the investigation "strongly favour" the theory of a bomb on board the plane but Moscow has not yet given any definitive cause for the disaster.

Separately, the Russian military said on Friday that its warplanes had struck 289 "terrorist" targets in 107 sorties over the past two days.

Moscow said it had destroyed 34 terrorist command centre and three training camps, among other targets.